---Research Outreach: "From red blood cells to a new concept for bio-devices'    Read more

Red blood cells zip through micron-wide capillaries almost friction-free, surviving hundreds of thousands of passages during their nearly 120-days lifespan. In this presentation, it will be shown that if we find a porous material with the same properties, we can apply this method in engineering applications and possibly make a breakthrough in designing micro, bio-devices, drug delivery systems, etc. Surprisingly, goose down has the same properties as our fiber-coated capillaries. More information: 1) 2) 3)

Experimental study of the flow over random porous media    Read more

Flow over porous media has significant applications in biological systems, and industrial processes. The main focus of the majority of works on this area has been on the formulation of appropriate conditions at the interface separating the pure fluid from the porous medium flow. Furthermore, recent experimental measurements have been limited to explore the flow over superhydrophic surfaces as well as homogenous patterns. Previous studies show that the drag force due to sliding friction can be dramatically reduced if the elastic restoring force of the solid phase is small compared to the lift force generated by transiently trapped air inside the porous material. In this study, particle image velocimetry (PIV) was used to observe slip velocities, shear stress, and drag reductions over a random soft porous media. Results illustrate the significant effect of these patterns on the streamlines, which can potentially affect drag force.

CFD modeling of particle migration in an eccentric cylinder using SBM    Read more

The suspension balance and diffusive flux models have been developed to explain the particle migration phenomenon. Here we use the suspension balance model (SBM) to provide numerical validation of the particle migration in a concentrated suspension undergoing flow between rotating eccentric cylinders observed in experiment of Subia et al. (1998). This study demonstrates that by implementing the mathematical model developed to explain particle migration phenomenon, namely SBM into available commercial software such as COMSOL, one can readily explore the behavior of these systems. A 2D finite element (FEM) model of the SBM has been created in COMSOL Multiphysics. A set of transient conservation equations of bulk and particle-phase mass and momentum that included gravitational force effects were solved using the implicit time-stepping method of backward differentiation. The simulation method was validated using the available analytical solution for suspension in a circular Couette flow. The eccentricity ratio has been defined as ε=e/(Ro-Ri), where Ro is the outer cylinder radius, Ri is the inner cylinder radius and e is the distance between the center of the inner and outer cylinders. Eccentricity ratio was analyzed and it was shown that for eccentricity ratio, ε<0.5 and particle volume fraction, φ=50%, the maximum concentration occurs circumferentially in the direction of the stationary cylinder. As ε increases and φ=50%, the maximum concentration appears along the horizontal mid-plane of the eccentric bearing in the wide-gap region. Further increases in the eccentricity ratio shift the maximum concentration region towards the rotating cylinder. The simulation results of concentration distribution and velocity profile compare well with the experimental data. This study provides a qualitative step forward in the application of computational fluid dynamics to suspension flows in various geometries and serves as a first step towards exploring the realistic 3D modeling of dense suspensions in eccentric bearings as an example of general geometries.

Analysis of the Bolus Formation from the Micropipette Ejection Systems    Read more

The ejection of drugs from micropipettes is practiced frequently in biomedical research and clinical studies however, little is known about the dynamics of this process. The fundamentals of disperse fluid injection via a capillary into an ambient immiscible fluid have been investigated extensively. Here, we experimentally investigate the bolus formation in micropipette ejection systems, where the injection and ambient fluid are the same. We experimentally measure the temporal evolution of the bolus formation in the same fluid. There are three different bolus formation mechanisms that arise from different Ret regimes: a) a nearly spherical bolus, b) a pear-like bolus, and c) a large distortion or axial jet. We examine the scaled dimensions of the bolus, Rb/Dt, Lb/Dt, H/Dt, and , as a function of the dimensionless parameters such as tip Reynolds number, Ret, dimensionless value of g/(Dt · Vt), the dimensionless time, tVt/Dt, and the distance between the edge of the micropipette and the free surface, D/Dt. The bolus radius for 0.2 < Ret < 30 grows according to t1/2 in the entire time range, which allows us to estimate the time for complete bolus formation.

Lift generation in Highly Compressible Porous media    Read more

My PhD thesis lied at the intersection of fluid mechanics and biology. The previous observations regarding the remarkable similarity between a human skiing on the snow powder and the motion of red cell passing through tightly fitting capillaries showed that the dimensionless permeability parameter α for a gliding motion of a red cell moving over the endothelial glycocalyx layer (EGL) and a human snowboarding on compressed powder is roughly 100, although they differ in mass by 15 orders of magnitude. The biggest difference between them is the huge loss of excess pore pressure from the lateral edges of the ski, thus the pressure and lift force decrease as (W/L)2 for large α where W is the width of the planning surface and L is the length. For a skier less than 40% of the lift comes from the air transiently trapped beneath ski due to this loss of pressure. This investigation, motivated the study of the generation of lift force in random, soft porous media. A lubrication theory for random, highly compressible porous media was developed and was shown that a huge lift force can be generated in random fibers that can be used in several applications such as slider bearings or commercial transportations, however, for its novelty we applied this enhanced lift force to design a new train track. Using an asymptotic analysis for large values of the permeability parameter, α=H/√Kp, where H is the porous layer thickness and Kp the Darcy permeability, the possibility to support a 70 metric ton jet train carrying 200 passengers on a confined porous material where its Kp is approximately 5 x 10-9 m2 was examined. This value of Kp can be satisfied by a random fiber matrix with a fiber radius of 5 µm and a void fraction of 0.995. Using jet engines of 10,000 lbf thrust, about 1/5 that of a 200 passenger jet aircraft, one is able to obtain a cruising velocity approaching 700 km/hr. This would allow for huge fuel savings, especially on short flights where much of the energy expenditure is used to climb to altitude and overcoming lift induced drag.